The present invention relates to a negative resist composition suitably used in an ultramicrolithography process or another photofabrication process for the production of very large-scale integrated circuits or high capacity microchips. More particularly, the invention relates to a negative resist composition which can form highly miniaturized patterns by use of X-rays or electron beams including excimer laser beams, and especially to a negative resist composition which can be suitably used in miniaturization processing of semiconductor elements by use of high energy beams such as electron beams.
Integrated circuits have been progressively increased in their integration degree, and therefore processing of ultra-micro patterns having a line width of a half micron or less has become necessary in the production of semiconductor substrates for very large-scale integrated circuits. For fulfilling this necessity, the wavelength of light used in an exposure apparatus employed for photolithography becomes progressively shorter, and now, far ultraviolet light and excimer laser light (such as XeCl, KrF or ArF) has been studied. Further, the formation of more micro patterns with electron beams or X-rays has been studied.
In particular, electron beams or X-rays are placed as next or next-next generation technology of pattern formation, and the development of negative resists which can attain high sensitivity, high resolution and rectangular profile shape has been desired.
Electron beam lithography is technology in which accelerated electron beams emit energy in the course of colliding with atoms constituting resist materials to cause scattering, thereby exposing the resist materials. The use of highly accelerated electron beams increases the rectilinear propagation and reduces the influence of electron scattering, which makes it possible to form rectangular patterns having high resolution. On the other hand, it increases the permeability of electron beams, resulting in lowered sensitivity. As described above, in the electron beam lithography, there is the trade-off relationship between the sensitivity and the resolution/resist shape, and it has been a problem how to allow them to be compatible with each other. With respect to chemical amplification type negative resists, various acid generators have hitherto been proposed. JP-B-8-3635 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d) discloses organic halogen compounds, JP-A-2-150848 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent application) and JP-A-6-199770 disclose iodonium salts and sulfonium salts, JP-A-2-52348, JP-A-4-367864 and JP-A-4-367865 disclose acid generators containing Cl or Br, JP-A-4-210960 and JP-A-4-217249 disclose diazodisulfone and diazosulfone compounds, JP-A-4-226454 discloses triazine compounds, and JP-A-3-87746, JP-A-4-291259, JP-A-6-236024 and U.S. Pat. No. 5,344,742 disclose sulfonate compounds. However, these acid generators have failed to overcome the trade-off relationship between the sensitivity and the resolution/resist shape under irradiation of electron beams.
As to crosslinking agents, methylolmelamine, resol resins, epoxidated novolak resins and urea resins have hitherto been used. However, these crosslinking agents are unstable to heat, so that they have a problem with regard to storage stability when used in resist solutions. Further, they have failed to satisfy required characteristics of high sensitivity, high resolution and rectangular resist shape under irradiation of electron beams.
It is therefore an object of the invention to solve the problems in respect to techniques for improving the original performance of the micro photofabrication using electron beams, and to develop chemical amplification system negative resist compositions for electron beams or X-rays satisfying the characteristics of sensitivity and resolution/resist shape to the use of the electron beams or the X-rays.
As a result of intensive studies, the present inventors have known that the above-mentioned various objects of the invention are attained by using specific photoacid generators and/or specific crosslinking agents, depending on the type of photosensitive composition, thus completing the invention.
That is to say, these and other objects of the invention are attained by the following:
(1) A chemical amplification system negative resist composition for an electron beam and/or an X-ray comprising an alkali-soluble resin, a radiation-sensitive acid generator and a crosslinking agent which initiates crosslinking by an acid, wherein the crosslinking agent is a phenol derivative having 3 to 5 benzene ring atomic groups in a molecule, having a molecular weight of 1,200 or less, and having two or more hydroxymethyl and/or alkoxymethyl groups in all in the molecule, the groups being combined with at least any of the benzene ring atomic groups;
(2) The negative resist composition according to claim 1, wherein the radiation-sensitive acid generator is a compound represented by any one of the following general formulas (I) to (III): 
wherein R1 to R37 each represents a hydrogen atom, an alkyl group, an alkoxyl group, a hydroxyl group, a halogen atom or a group represented by xe2x80x94Sxe2x80x94R38 wherein R38 represents an alkyl group or an aryl group; R1 to R38 may be the same or different; two or more selected from R1 to R15 may be combined with each other directly at their ends, or through an atom selected from oxygen, sulfur and nitrogen to form a ring structure; R16 to R27 may also form a ring structure similarly; R28 to R37 may also form a ring structure similarly; Xxe2x88x92 is an anion of an acid, which is selected from benzenesulfonic acid, naphthalene-sulfonic acid and anthracenesulfonic acid; the acid is substituted by a fluorine atom, and has at least one organic group selected from the group consisting of an alkyl group, an alkoxyl group, an acyl group, an acyloxy group, a sulfonyl group, a sulfonyloxy group, a sulfonylamino group, an aryl group, an aralkyl group and an alkoxycarbonyl group; and moreover, the organic group is further substituted by at least one fluorine atom; and
(3) The negative resist composition according to claim 2, wherein each of the alkyl group and the alkoxyl group is any one of straight-chain, branched or cyclic groups.
Embodiments of the negative resist compositions of the invention include (1) and (2) described below:
(1) A negative resist composition comprising an alkali-soluble resin, a radiation-sensitive acid generator and a crosslinking agent, in which the crosslinking agent is a phenol derivative having 3 to 5 benzene ring atomic groups in a molecule, having a molecular weight of 1,200 or less, and having two or more hydroxymethyl and/or alkoxymethyl groups in all in the molecule, the groups being combined with at least any of the benzene ring atomic groups, and initiates crosslinking by an acid; and
(2) A negative resist composition comprising an alkali-soluble resin, a radiation-sensitive acid generator represented by any one of general formulas (I) to (III) and a crosslinking agent, in which the crosslinking agent is a phenol derivative having 3 to 5 benzene ring atomic groups in a molecule, having a molecular weight of 1,200 or less, and having two or more hydroxymethyl and/or alkoxymethyl groups in all in the molecule, the groups being combined with at least any of the benzene ring atomic groups, and initiates crosslinking by an acid.
In the invention, of the above-mentioned embodiments (1) and (2), the embodiment (1) is preferred in that the effects of the invention are achieved more significantly.
The compounds used in the invention are described below:
(1) Alkali-Soluble Resins Used in the Invention
In the invention, the alkali-soluble resins are used together with the radiation-sensitive acid generators. Examples of the alkali-soluble resins used together with the radiation-sensitive acid generators include but are not limited to novolak resins, hydrogenated novolak resins, acetone-pyrogallol resins, poly-o-hydroxystyrene, poly-m-hydroxystyrene, poly-p-hydroxystyrene, hydrogenated poly-hydroxystyrene, halogen- or alkyl-substituted polyhydroxy-styrenes, hydroxystyrene-N-substituted maleimide copolymers, o/p- and m/p-hydroxystyrene copolymers, products partially O-alkylated to hydroxyl groups of polyhydroxystyrene (e.g., 5 to 30 mol % O-methylated products, O-(1-methoxy)ethylated products, O-(1-ethoxy)ethylated products, O-2-tetrahydro-pyranylated products and O-(t-butoxycarbonyl)methylated products), or O-acylated products (e.g., 5 to 30 mol % O-acetylated products and O-(t-butoxy)carbonylated products), styrene-maleic anhydride copolymers, styrene-hydroxystyrene copolymers, xcex1-methylstyrene-hydroxystyrene copolymers, carboxyl group-containing methacrylic resins and derivatives thereof.
Of the above-mentioned alkali-soluble resins, particularly preferred are novolak resins, poly-o-hydroxystyrene, poly-m-hydroxystyrene, poly-p-hydroxystyrene and copolymers thereof, alkyl-substituted polyhydroxy-styrenes, partially O-alkylated or O-acylated products of polyhydroxystyrene, styrene-hydroxystyrene copolymers and xcex1-methylstyrene-hydroxystyrene copolymers.
The novolak resins are obtained by addition condensation of specified monomers as main components with aldehydes in the presence of acidic catalysts.
The specified monomers include but are not limited to phenols, cresols such as m-cresol, p-cresol and o-cresol, xylenols such as 2,5-xylenol, 3,5-xylenol, 3,4-xylenol and 2,3-xylenol, alkylphenols such as m-ethylphenol, p-ethylphenol, o-ethylphenol, p-t-butylphenol, p-octylphenol and 2,3,5-trimethylphenol, alkoxyphenols such as p-methoxyphenol, m-methoxyphenol, 3,5-dimethoxyphenol, 2-methoxy-4-methylphenol, m-ethoxyphenol, p-ethoxyphenol, m-propoxyphenol, p-propoxyphenol, m-butoxyphenol and p-butoxyphenol, bisalkylphenols such as 2-methyl-4-isopropylphenol, and hydroxy aromatic compounds such as m-chlorophenol, p-chlorophenol, o-chlorophenol, dihydroxybiphenyl, bisphenol A, phenylphenol, resorcinol and naphthol. These monomers can be used either alone or as a combination of two or more of them.
The aldehydes include, for example, formaldehyde, paraformaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, phenylacetaldehyde, xcex1-phenylpropylaldehyde, xcex2-phenylpropylaldehyde, o-hydroxybenzaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde, o-chlorobenzaldehyde, m-chlorobenzaldehyde, p-chlorobenzaldehyde, o-nitrobenzaldehyde, m-nitrobenzaldehyde, p-nitrobenzaldehyde, o-methylbenzaldehyde, m-methylbenzaldehyde, p-methylbenzaldehyde, p-ethylbenzaldehyde, p-n-butylbenzaldehyde, furfural, chloroacetaldehyde and acetals thereof such as chloroacetaldehyde diethylacetal. Of these, formaldehyde is preferably used.
These aldehydes are used either alone or as a combination of two or more of them. As the acidic catalysts, hydrochloric acid, sulfuric acid, formic acid, acetic acid and oxalic acid can be used.
It is preferred that the novolak resins thus obtained have a weight-average molecular weight ranging from 1,000 to 30,000. Less than 1,000 causes an increase in the film thickness loss of exposed areas after development, whereas exceeding 30,000 results in decreased developing speed. The particularly preferred range is from 2,000 to 20,000.
Further, the weight-average molecular weight of polyhydroxystyrene, the derivatives thereof and the copolymers thereof other than the novolak resins is 2,000 or more, preferably from 2,000 to 30,000, and more preferably from 2,000 to 20,000.
The weight-average molecular weight as used herein is defined as a value measured by gel permeation chromatography and reduced to the weight-average molecular weight of polystyrene.
The rate of alkali dissolution of the alkali-soluble resins is preferably 20 xc3x85/second or more, and particularly preferably 200 xc3x85/second or more, when measured in 0.261 N tetramethylammonium hydroxide (TMAH) at 23xc2x0 C.
In the present invention, these alkali-soluble resins may be used either alone or as a combination of two or more of them.
The alkali-soluble resins are used usually in an amount of 30% to 90% by weight, and preferably in an amount of 50% to 80% by weight, based on the total weight of resist composition (excluding solvents).
(2) Radiation-Sensitive Acid Generators (hereinafter also referred to as Photoacid Generators)
The radiation-sensitive acid generators are used together with the alkali-soluble resins. The radiation-sensitive acid generators used together with the alkali-soluble resins are represented by the above-mentioned general formulas (I) to (III).
R1 to R37 in general formulas (I) to (III) each represents an alkyl group, an alkoxyl group, a hydroxyl group, a halogen atom or a group represented by xe2x80x94Sxe2x80x94R38.
The alkyl groups represented by R1 to R37 may be straight-chain, branched or cyclic. The straight-chain or branched alkyl groups include, for example, alkyl groups each having 1 to 4 carbon atoms such as methyl, ethyl, propyl, n-butyl, sec-butyl and t-butyl. The cyclic alkyl groups include, for example, alkyl groups each having 3 to 8 carbon atoms such as cyclopropyl, cyclopentyl and cyclohexyl.
The alkoxyl groups represented by R1 to R37 may be straight-chain, branched or cyclic. The straight-chain or branched alkoxyl groups include, for example, alkoxyl groups each having 1 to 8 carbon atoms such as methoxy, ethoxy, hydroxyethoxy, propoxy, n-butoxy, isobutoxy, sec-butoxy, t-butoxy and octyloxy. The cyclic alkoxyl groups include, for example, cyclopentyloxy and cyclohexyloxy.
The halogen atoms represented by R1 to R37 include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.
R38 in xe2x80x94Sxe2x80x94R38 represented by R1 to R37 is an alkyl group or an aryl group. The alkyl groups represented by R38 include, for example, ones already enumerated as the alkyl groups represented by R1 to R37.
The aryl groups represented by R38 include aryl groups each having 6 to 14 carbon atoms such as phenyl, tolyl, methoxyphenyl and naphthyl.
Any one of the groups represented by R1 to R38 may further be combined with a substituent to increase the carbon number, or have no substituent. Preferred examples of the substituents with which the groups may further be combined include alkoxyl groups each having 1 to 4 carbon atoms, aryl groups each having 6 to 10 carbon atoms and alkenyl groups each having 2 t 6 carbon atoms such as cyano, hydroxyl, carboxyl, alkoxycarbonyl and nitro. In addition, the substituents may be halogen atoms such as fluorine, chlorine and iodine.
Two or more of the groups represented by R1 to R15 in general formula (I) may be combined to form a ring. The groups represented by R1 to R15 may be combined with each other directly at their ends, or indirectly through at least one atom selected from carbon, oxygen, sulfur and nitrogen to form the ring. The ring structures formed by combination of two or more of R1 to R15 include the same structures as the ring structures seen in furan, dihydrofuran, pyran, trihydropyran, thiophene and pyrrole rings. R16 to R27 in general formula (II) are similar to the above. Two or more of them may be combined directly or indirectly with each other to form a ring. R28 to R37 in general formula (III) are also similar thereto.
General formulas (I) to (III) have Xxe2x88x92, which is an anion of an acid. The acid which forms the anion is an acid selected from benzenesulfonic acid, naphthalenesulfonic acid and anthracenesulfonic acid. The acid is substituted by at least one fluorine atom, or has at least one organic group selected from the group consisting of an alkyl group, an alkoxyl group, an acyl group, an acyloxy group, a sulfonyl group, a sulfonyloxy group, a sulfonylamino group, an aryl group, an aralkyl group and an alkoxycarbonyl group, together with or instead of the fluorine atom. Moreover, the organic group is further substituted by at least one fluorine atom. The above-mentioned benzenesulfonic acid, naphthalenesulfonic acid or anthracenesulfonic acid may be substituted by a halogen atom other than fluorine, a hydroxyl group or a nitro group.
The alkyl groups combined with benzenesulfonic acid or the like which forms the Xxe2x88x92 anion are, for example, alkyl groups each having 1 to 12 carbon atoms. The alkyl groups may be straight-chain, branched or cyclic. They are each substituted by at least one fluorine atom, preferably 25 or less fluorine atoms. Specific examples thereof include trifluoromethyl, pentafluoroethyl, 2,2,2-trifluoroethyl, heptafluoropropyl, heptafluoroisopropyl, perfluorobutyl, perfluorooctyl, perfluorododecyl and perfluorocyclohexyl. Perfluoroalkyl groups each having 1 to 4 carbon atoms in which all are substituted by fluorine atoms are preferred among others.
The alkoxyl groups combined with benzenesulfonic acid or the like described above, together with or independently of the alkyl groups, are alkoxyl groups each having 1 to 12 carbon atoms. The alkoxyl groups may be straight-chain, branched or cyclic. They are each substituted by at least one fluorine atom, preferably 25 or less fluorine atoms. Specific examples thereof include trifluoromethoxy, pentafluoroethoxy, heptafluoroisopropyloxy, perfluorobutoxy, perfluorooctyloxy, perfluorododecyloxy and perfluorocyclohexyloxy. Perfluoroalkoxyl groups each having 1 to 4 carbon atoms in which all are substituted by fluorine atoms are preferred among others.
The acyl groups combined with benzenesulfonic acid or the like described above, together with or independently of the alkyl groups, are preferably acyl groups each having 2 to 12 carbon atoms and substituted by 1 to 23 fluorine atoms. Specific examples thereof include trifluoroacetyl, fluoroacetyl, pentafluoropropionyl and pentafluorobenzoyl.
The acyloxy groups combined with benzenesulfonic acid or the like described above, together with or independently of the alkyl groups, are preferably acyloxy groups each having 2 to 12 carbon atoms and substituted by 1 to 23 fluorine atoms. Specific examples thereof include trifluoroacetoxy, fluoroacetoxy, pentafluoropropionyloxy and pentafluorobenzoyloxy.
The sulfonyl groups combined with benzenesulfonic acid or the like described above, together with or independently of the alkyl groups, are preferably sulfonyl groups each having 1 to 12 carbon atoms and substituted by 1 to 25 fluorine atoms. Specific examples thereof include trifluoromethanesulfonyl, pentafluoroethanesulfonyl, perfluorobutanesulfonyl, perfluorooctanesulfonyl, pentafluorobenzenesulfonyl and 4-trifluoromethylbenzenesulfonyl.
The sulfonyloxy groups combined with benzenesulfonic acid or the like described above, together with or independently of the alkyl groups, are preferably sulfonyloxy groups each having 1 to 12 carbon atoms and substituted by 1 to 25 fluorine atoms. Specific examples thereof include trifluoro-methanesulfonyloxy, perfluorobutanesulfonyloxy and 4-trifluoromethylbenzenesulfonyloxy.
The sulfonylamino groups combined with benzenesulfonic acid or the like described above, together with or independently of the alkyl groups, are preferably sulfonylamino groups each having 1 to 12 carbon atoms and substituted by 1 to 25 fluorine atoms. Specific examples thereof include trifluoromethanesulfonylamino, perfluorobutanesulfonylamino, perfluorooctanesulfonylamino and pentafluorobenzenesulfonylamino.
The aryl groups combined with benzenesulfonic acid or the like described above, together with or independently of the alkyl groups, are preferably aryl groups each having 6 to 14 carbon atoms and substituted by 1 to 9 fluorine atoms. Specific examples thereof include pentafluorophenyl, 4-trifluoromethylphenyl, heptafluoronaphthyl, nonafluoro-anthranyl, 4-fluorophenyl and 2,4-difluorophenyl.
The aralkyl groups combined with benzenesulfonic acid or the like described above, together with or independently of the alkyl groups, are preferably aralkyl groups each having 7 to 10 carbon atoms and substituted by 1 to 15 fluorine atoms. Specific examples thereof include pentafluorophenylmethyl, pentafluorophenylethyl, perfluorobenzyl and perfluorophenethyl.
The alkoxycarbonyl groups combined with benzenesulfonic acid or the like described above, together with or independently of the alkyl groups, are preferably alkoxycarbonyl groups each having 2 to 13 carbon atoms and substituted by 1 to 25 fluorine atoms. Specific examples thereof include trifluoromethoxycarbonyl, pentafluoroethoxycarbonyl, pentafluorophenoxycarbonyl, perfluorobutoxycarbonyl and perfluorooctyloxycarbonyl.
Of such Xxe2x88x92 anions, most preferred is a fluorine-substituted benzenesulfonic acid anion, and a pentafluoro-benzenesulfonic acid anion is particularly preferred among others.
In addition, benzenesulfonic acid, naphthalenesulfonic acid or anthracenesulfonic acid having the above-mentioned fluorine-containing substituent may be further substituted by a straight-chain, branched or cyclic alkoxyl group, an acyl group, an acyloxy group, a sulfonyl group, a sulfonyloxy group, a sulfonylamino group, an aryl group, an aralkyl group, an alkoxycarbonyl group (the carbon number range of these groups is the same as described above), a halogen atom (extruding fluorine), a hydroxyl group or a nitro group.
Specific examples of these compounds represented by general formulas (I) to (III) are shown below, but are not limited thereto. 
The compounds of general formulas (I) and (II) can be synthesized by the following processes. For example, aryl Grignad reagents such as arylmagnesium bromides are reacted with phenyl sulfoxides to obtain triarylsulfonium halides, and the salt interchange thereof with sulfonic acids corresponding thereto is conducted. As another process, the condensation and salt interchange of phenyl sulfoxides with aromatic compounds corresponding thereto are conducted using acid catalysts such as methanesulfonic acid/diphosphorus pentaoxide or aluminum chloride. Further, the compounds can be synthesized by a process in which the condensation and salt interchange of diaryliodonium salts with diaryl sulfides are conducted using catalysts such as copper acetate. In any one of the above-mentioned processes, the phenyl sulfoxides may have substituents at benzene rings, or may not have such substituents.
The compounds of general formula (III) can be synthesized by reacting aromatic compounds using periodates.
The amount of the photoacid generators used in the invention is suitably from 0.1% to 20% by weight, preferably from 0.5% to 10% by weight, and more preferably from 1% to 7% by weight, based on the total solid content of negative resist composition.
When the compounds represented by any one of general formulas (I) to (III) are contained as the radiation-sensitive acid generators, the content thereof is suitably from 0.1% to 20% by weight, preferably from 0.5% to 10% by weight, and more preferably from 1% to 7% by weight, based on the total solid content of negative resist composition.
(Other Photoacid Generators)
In the invention, other compounds which are decomposed by radiation irradiation to generate acids can be used, except or together with the compounds represented by general formulas (I) to (III). When the other compounds which are decomposed by radiation irradiation to generate acids are used except or together with the compounds represented by general formulas (I) to (III), the ratio of the other compounds which are decomposed by radiation irradiation to generate acids to the compounds represented by general formulas (I) to (III) is from 100/0 to 20/80, preferably from 90/10 to 40/60, and more preferably from 80/20 to 50/50, in molar ratio.
As such other photoacid generators, photo-initiators for cationic photopolymerization, photoinitiators for radical photopolymerization, photodecoloring agents and photodiscloring agents for dyes, known photoacid generating compounds used in micro resists and mixtures thereof can be appropriately selected to use them.
Examples thereof include onium salts such as diazonium salts, phosphonium salts, iodonium salts, sulfonium salts, selenonium salts and arsonium salts, organic halogen compounds, organic metal/organic halides, photoacid generators having o-nitrobenzyl type protective groups, compounds producing sulfonic acids by photolysis, which are represented by iminosulfonates, and disulfone compounds.
Further, compounds in which these photoacid generating groups or compounds are introduced into their main chains or side chains, for example, compounds described in JP-A-63-26653, JP-A-55-164824, JP-A-62-69263, JP-A-63-146038, JP-A-63-163452, JP-A-62-153853 and JP-A-63-146029, can be used.
Furthermore, photoacid generating compounds described in U.S. Pat. No. 3,779,778 and European Patent 126,712 can also be used.
(3) Crosslinking Agents Used in the Invention
In the negative resist compositions of the invention, compounds crosslinking by acids (hereinafter referred to as acid-crosslinking agents or briefly crosslinking agents) are used together with the photoacid generators.
As the crosslinking agents, phenol derivatives can be used. Examples thereof include phenol derivatives having a molecular weight of 1,200 or less, each containing 3 to 5 benzene rings in a molecule and each having two or more of hydroxymethyl groups or alkoxymethyl groups in all, in which the hydroxymethyl groups or alkoxymethyl groups are bonded collectively to at least any one of the benzene rings, or divisionally to the benzene rings.
The alkoxymethyl groups bonded to the benzene rings are preferably alkoxymethyl groups each having 6 or less carbon atoms. Preferred examples thereof include methoxymethyl, ethoxymethyl, n-propoxymethyl, i-propoxymethyl, n-butoxymethyl, i-butoxymethyl, sec-butoxymethyl and t-butoxymethyl. Further, alkoxy-substituted alkoxyl groups such as 2-methoxyethoxy and 2-methoxy-1-propyl are also preferred.
Of these phenol derivatives, particularly preferred ones are shown below: 
wherein L1 to L8, which may be the same or different, each represents a hydroxymethyl group, a methoxymethyl group or an ethoxymethyl group.
The phenol derivatives having hydroxymethyl groups can be obtained by reacting corresponding phenol compounds having no hydroxymethyl groups (compounds in which L1 to L8 are hydrogen atoms in the above formulas) with formaldehyde in the presence of base catalysts. In this case, the reaction is preferably conducted at a temperature of 60xc2x0 C. or less, for preventing resinification and gelation. Specifically, they can be synthesized by methods described in JP-A-6-282067 and JP-A-7-64285.
The phenol derivatives having alkoxymethyl groups can be obtained by reacting corresponding phenol derivatives having hydroxymethyl groups with alcohols in the presence of acid catalysts. In this case, the reaction is preferably conducted at a temperature of 100xc2x0 C. or less, for preventing resinification and gelation. Specifically, they can be synthesized by methods described in EP-A-632,003.
The hydroxymethyl group- or alkoxymethyl group-containing phenol derivatives thus synthesized are preferred in respect to stability in storage, and the alkoxymethyl group-containing phenol derivatives are particularly preferred from the viewpoint of stability in storage.
These phenol derivatives each having two or more of hydroxym ethyl groups or alkoxymethyl groups in all, in which the hydroxymethyl groups or alkoxymethyl groups are bonded collectively to at least any one of the benzene rings, or divisionally to the benzene rings, may be used either alone or as a combination of two or more of them.
Such phenol derivatives are used in an amount of 3% to 70% by weight, and preferably in an amount of 5% to 50% by weight, based on the total solid content of resist composition. When the phenol derivatives are added as the crosslinking agents in an amount of less than 3% by weight, the residual film rate is decreased. On the other hand, exceeding 70% by weight results in reduced resolution, and further unfavorably leads to deteriorated stability in storage of resist solutions.
In the invention, for example, the following other crosslinking agents (i) and (ii) are preferably used in combination with the above-mentioned phenol derivatives.
The ratio of the other crosslinking agents to the phenol derivatives is from 100/0 to 20/80, preferably from 90/10 to 40/60, and more preferably from 80/20 to 50/50, in molar ratio.
(i) Compounds having N-hydroxymethyl groups, N-alkoxymethyl groups or N-acyloxymethyl groups; and
(ii) Epoxy compounds.
These crosslinking agents are described in detail below.
(i) The compounds having N-hydroxymethyl groups, N-alkoxymethyl groups or N-acyloxymethyl groups include monomer/oligomer-melamine-formaldehyde condensation products and urea-formaldehyde condensation products disclosed in EP-A-0,133,216, West German Patents 3,634,671 and 3,711,264, and benzoguanamine-formaldehyde condensation products disclosed in EP-A-0,212,482.
More preferred examples thereof include melamine-formaldehyde condensation products each having at least two free N-hydroxymethyl groups, N-alkoxymethyl groups or N-acyloxymethyl groups, and the N-alkoxymethyl derivatives are particularly preferred among others.
(ii) The epoxy compounds include monomers, dimers, oligomers and polymers of epoxy compounds each having at least one epoxy group. Examples thereof include reaction products of bisphenol A and epichlorohydrin, reaction products of low molecular weight phenol-formaldehyde resins and epichlorohydrin, and further epoxy resins described and used in U.S. Pat. No. 4,026,705 and British Patent 1,539,192.
(4) Other Components Used in Compositions of the Invention
The negative resist compositions of the invention can further contain organic basic compounds, dyes and surfactants as needed.
(4)-1 Dyes
The suitable dyes are oil dyes and basic dyes. Specific examples thereof include Oil Yellow #101, Oil Yellow #103, Oil Pink #312, Oil Green BG, Oil Blue BOS, Oil Blue #603, Oil Black BY, Oil Black BS, Oil Black T-505 (the above dyes are manufactured by Orient Kagaku Kogyo Co., Ltd.), Crystal Violet (CI42555), Methyl Violet (CI42535), Rhodamine B (CI45170B), Malachite Green (CI42000) and Methylene Blue (CI52015).
(4)-2 Organic Basic Compounds
The organic basic compounds which can be used in the invention are preferably compounds stronger in basicity than phenol, and nitrogen-containing basic compounds are preferred among others.
Preferred examples thereof include compounds having structures represented by the following formulas (A) to (E): 
wherein
R250, R251 and R252, which may be the same or different, each represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an aminoalkyl group having 1 to 6 carbon atoms, a hydroxyalkyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, and R251 and R252 may combine with each other to form a ring.
R253, R254, R255 and R256, which may be the same or different, each represents an alkyl group having 1 to 6 carbon atoms.
More preferred are nitrogen-containing basic compounds each having two or more nitrogen atoms different in chemical environment in one molecule, and particularly preferred are compounds each having both a substituted or unsubstituted amino group and a nitrogen atom-containing ring structure, or compounds each having an alkylamino group.
Preferred examples thereof include substituted or unsubstituted guanidine, substituted or unsubstituted aminopyridine, substituted or unsubstituted aminoalkylpyridines, substituted or unsubstituted aminopyrrolidine, substituted or unsubstituted indazole, imidazole, substituted or unsubstituted pyrazole, substituted or unsubstituted pyrazine, substituted or unsubstituted pyrimidine, substituted or unsubstituted purine, substituted or unsubstituted imidazoline, substituted or unsubstituted pyrazoline, substituted or unsubstituted piperazine, substituted or unsubstituted aminomorpholine and substituted or unsubstituted aminoalkylmorpholines. Preferred substituents are amino, aminoalkyl, alkylamino, aminoaryl, arylamino, alkyl, alkoxyl, acyl, acyloxy, aryl, aryloxy, nitro, hydroxyl and cyano.
Particularly preferred examples of the compounds include but are not limited to guanidine, 1,1-dimethylguanidine, 1,1,3,3-tetramethylguanidine, imidazole, 2-methylimidazole, 4-methylimidazole, N-methylimidazole, 2-phenylimidazole, 4,5-diphenylimidazole, 2,4,5-triphenylimidazole, 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 2-dimethylaminopyridine, 4-dimethylaminopyridine, 2-diethylaminopyridine, 2-(aminomethyl)pyridine, 2-amino-3-methylpyridine, 2-amino-4-methylpyridine, 2-amino-5-methylpyridine, 2-amino-6-methyl-pyridine, 3-aminoethylpyridine, 4-aminoethylpyridine, 3-aminopyrrolidine, piperazine, N-(2-aminoethyl)piperazine, N-(2-aminoethyl)piperidine, 4-amino-2,2,6,6-tetramethyl-piperidine, 4-piperidinopiperidine, 2-iminopiperidine, 1-(2-aminoethyl)pyrrolidine, pyrazole, 3-amino-5-methylpyrazole, 5-amino-3-methyl-1-p-tolylpyrazole, pyrazine, 2-(amino-methyl)-5-methylpyrazine, pyrimidine, 2,4-diaminopyrimidine, 4,6-dihydroxypyrimidine, 2-pyrazoline, 3-pyrazoline, N-aminomorpholine and N-(2-aminoethyl)morpholine.
These nitrogen-containing basic compounds are used either alone or as a combination of two or more of them. The ratio of the photoacid generator to the organic basic compound used in the composition ((photoacid generator)/(organic basic compound), molar ratio) is preferably from 2.5 to 300. When the molar ratio is less than 2.5, the sensitivity is decreased to cause a reduction in resolution in some cases. On the other hand, when the ratio exceeds 300, the resist pattern grows thick with an elapse of time from exposure to heat treatment to cause a reduction in resolution in some cases. The ratio ((photoacid generator)/(organic basic compound), molar ratio) is preferably from 5.0 to 200, and more preferably from 7.0 to 150.
(4)-3 Solvents
The photosensitive compositions of the invention are dissolved in solvents which can dissolve the above-mentioned respective components, and applied onto supports. Preferred examples of the solvents used herein include diethylene dichloride, cyclohexanone, cyclopentanone, 2-heptanone, xcex3-butyrolactone, methyl ethyl ketone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 2-methoxyethyl acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, toluene, ethyl acetate, methyl lactate, ethyl lactate, methyl methoxypropionate, ethyl ethoxypropionate, methyl pyruvate, ethyl pyruvate, propyl pyruvate, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone and tetrahydrofuran. These solvents are used either alone or as a mixture thereof.
(4)-4 Surfactants
Surfactants can also be added to the above-mentioned solvents. Specific examples of such surfactants include nonionic surfactants such as polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene cetyl ether and polyoxyethylene oleyl ether, polyoxyethylene alkyl allyl ethers such as polyoxyethylene octylphenol ether and polyoxyethylene nonyl-phenol ether, polyoxyethylene-polyoxypropylene block copolymers, sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, sorbitan trioleate and sorbitan tristearate, and polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan trioleate and polyoxyethylene sorbitan tristearate; fluorine surfactants such as EFTOP EF301, EF303 and EF352 (manufactured by Shin-Akita Kasei K.K.), MEGAFAC F171 and F173 (manufactured by Dainippon Ink and Chemicals, Inc.), FLORAD FC430 and FC431 (manufactured by Sumitomo 3M Co., Ltd.), and ASAHIGUARD AG710, SURFLON S-382, SC101, SC102, SC103, SC104, SC105 and SC106 (manufactured by Asahi Glass Company Ltd.); Organopolysiloxane Polymer KP-341 (manufactured by Shin-Etsu Chemical Co., Ltd.); and acrylic or methacrylic (co)polymers, POLYFLOW No. 75 and No. 95 (manufactured by Kyoeisha Yushi Kagaku Kogyo K.K.).
The amount of the surfactants compounded is usually 2 parts or less by weight, and preferably 1 part or less by weight, per 100 parts by weight of the solid components contained in the composition of the invention.
These surfactants can be added either alone or as a combination of some of them.
In the pattern formation process on resist films in the production of precision integrated circuit elements, the negative photoresist compositions of the invention are applied onto substrates (e.g., transparent substrates such as silicon/silicon dioxide coatings, glass substrates and ITO substrates), and then irradiated using an electron beam lithography system, followed by heating, development, rinsing and drying, thereby being able to form good resist patterns.
Developing solutions which can be used for developing the negative photoresist compositions of the invention include aqueous solutions of inorganic alkalis such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate and aqueous ammonia; primary amines such as ethylamine and n-propylamine; secondary amines such as diethylamine and di-n-butylamine; tertiary amines such as triethylamine and methyldiethylamine; alcohol amines such as dimethylethanolamine and triethanolamine; quaternary ammonium salts such as tetramethylammonium hydroxide, tetraethylammonium hydroxide and choline; and cyclic amines such as pyrrole and piperidine.
Further, alcohols such as isopropyl alcohol and/or surfactants such as nonionic surfactants can also be added in appropriate amounts to the aqueous solutions of the above-mentioned alkalis.
Of these developing solutions, preferred are the quaternary ammonium salts, and more preferred are tetramethylammonium hydroxide and choline.